The objective of this project is to characterize dose-response relationships, toxicity, and carcinogenic potential of tetrahydrofuran administered by inhalation to rats and mice in 2-year chronic studies following a 14-day pilot study. Animals will be exposed for 6 hours per day, 5 days per week for 2 years. A 65-week interim sacrifice, including hematology and histopathology, will be performed in the chronic study. At the end of two years, all animals will be given gross and microscopic histopathologic evaluations.